1. Field of the Invention
The present invention relates to an electric motor for a feed pump. Specifically, the present invention is directed to a fuel pump for a motor vehicle, the electric motor having a rotor and a stator with at least two magnetic shells and a spring element for prestressing the magnetic shells in order to hold them in their desired position within a housing.
2. Description of the Related Art
Electric motors are typically used in present-day fuel pumps or for driving cooling-fluid pumps or oil pumps and various designs are generally known in practice. In this context, the electric motor forms with the feed pump a pre-assemblable structural feed unit. The fluid to be fed flows mostly through the electric motor, so that the feed unit has a highly compact design.
One example of such an electric motor is found in DE 196 52 085 A1, wherein the magnetic shells are pressed by a spring element against stops arranged on a tubular housing. The spring element is manufactured from a bandlike or wirelike spring material.
One disadvantage of the known electric motor is that, on account of the stops and the spring element, the stator has a plurality of steps directed toward the rotor. When the electric motor is used in the feed pump and has the fluid flowing through it, the steps cause turbulence in the fluid. The turbulence leads to the formation of gas bubbles and to a reduction in the efficiency of the feed pump. One problem to which the present invention is directed is the design of an electric motor of the type initially mentioned which, when used as a feed pump, it generates particularly low turbulence in the fluid flow.
In the present invention, this problem is solved by providing a gap that is approximately the same width as the spacing between the magnetic shells and the rotor between the spring element and the rotor. By virtue of this design, an approximately annular gap of essentially uniform thickness is located between the stator and the rotor. Consequently, turbulence in the flow between the rotor and the stator are kept particularly low. The pressure loss during the flow of the medium through the electric motor is thereby reduced. As a result, the pump according to the invention has particularly high efficiency. Furthermore, the reduction in the turbulence in the flow leads to particularly low noise emission from the feed unit provided with the electric motor according to the invention.
The electric motor according to the invention requires particularly few components to be assembled, if the spring element has, toward the rotor, an essentially smooth face arranged level with the radially inner boundary of the magnetic shells. By virtue of this design, the radially inner face of the magnetic shells is continued by the spring elements, so that the stator, on its side facing the rotor, has a face which is flush with the magnetic shells. Turbulence in the flow can therefore be kept particularly low. This leads to a pronounced reduction in the formation of gas bubbles in the flow and to a particularly high efficiency for the feed pump.
In the case of a single spring element for holding two magnetic shells, turbulence within the flow can be kept particularly low if stops of the housing of the stator, which are provided for supporting the magnetic shells, are concealed by a diaphragm. According to an advantageous development of the invention, the turbulence in the flow are kept particularly low if the spring element and the diaphragm for the stops extend over the entire length of the magnetic shells.
The spring element of the known electric motor could be provided with a diaphragm, for example that is level with the radially inner boundary of the magnetic shells. This leads, however, to a complicated design for the spring element.
Furthermore, the diaphragm would have to be secured against release from the spring element, since a separation of the diaphragm and spring element may cause a blockage of the electric motor. According to another advantageous development of the invention, the spring element does not require a diaphragm to be additionally assembled if the spring element has an arcuate portion designed to correspond to the radially inner boundary of the magnetic shells, and if legs led radially outward are arranged on the two sides of the arcuate portion which face the magnetic shells.
According to another advantageous development of the invention, the spring element can be assembled in a particularly simple way if free ends of the legs are angled so as to point toward one another. According to another advantageous development of the invention, the spring element is fixed reliably in an intended position in the stator if the spring element has a C-shaped portion bearing with a middle region on a tubular housing, and if a diaphragm is arranged, in the region level with the magnetic shells, at one end of the C-shaped portion. By virtue of this design, the spring element is prestressed radially outward due to its inherent elasticity.
According to another advantageous development of the invention, the free end of the diaphragm is held reliably in its intended position distant from the rotor, if the diaphragm is designed to be supported on the second free end of the C-shaped portion. According to another advantageous development of the invention, the spring element has particularly high stability if the diaphragm has a web supported radially on the outside.
According to another advantageous development of the invention, the stator can be designed to be particularly smooth on its side facing the rotor, if the spring element is formed as a plastic molding. The spring element formed as a plastic molding could, for example, be of tubular design and the necessary prestress could be generated by virtue of the shape of its wall. However, according to another advantageous development of the invention, the plastic molding has a particularly simple design if the spring element in the form of a plastic molding is solid. The magnetic shells are thereby stressed into their intended position as a result of the elasticity of the material of the plastic molding.
As in the known electric motor, the spring element could prestress the magnetic shells against stops of the stator. A disadvantage of this design, however, is that, in order to avoid turbulence, the stops have to be covered with a diaphragm to be assembled separately. The electric motor according to the invention has a particularly simple design, however, if a plurality of spring elements for prestressing the magnetic shells against the housing are provided so as to correspond to the number of magnetic shells. By virtue of this design, a spring element is arranged in each case at mutually opposite lateral boundaries of the magnetic shells, so that, in the simplest instance, the stator does not require any stop for the magnetic shells. Since, for example in the case of two magnetic shells, the stator consequently also has two spring elements, long prestressing excursions, along with low deformations of the spring elements in each case, can be achieved.
The invention permits numerous embodiments. In order to make its basic principal even clearer, several of these are illustrated in the drawing and are described below with reference to the drawings wherein: